bug(#266): sparse-free-decoration in application

[h1alexbel]

In this PR, I've updated sparse-decoration.xsl so that it doesn't issue defects in the object application.

see #266
History:

• bug(sparse-decoration complains too much #266): tests
• bug(sparse-decoration complains too much #266): allows in application

[h1alexbel]

@yegor256 please check

[yegor256]

@maxonfjvipon please, check this one

[maxonfjvipon]

@h1alexbel I suggest we put this PR on hold until we resolve this. There are some breaking changes which may affect this PR

[h1alexbel]

@maxonfjvipon synced PR with EO 0.51.1. Take a look, please

[maxonfjvipon]

@h1alexbel the idea of sparse decoration is simple - don't use abstract objects if you can.
Consider the example:

[] > foo
  5 > @

Here we can get rid of abstract object:

5 > foo

The same story with:

[] > foo
  x y z > @

It'll be

x y z > foo

But here we can't just get rid of it because of void attribute:

[x] > foo
  5 > @

The same story here:

[] > foo
  5 > @
  4 > x

So the main idea - if abstract object has only one attribute and it has name @ - it's sparse decoration.

Considering this let's simplify the whole condition with something like this:

//o[eo:abstract(.) and count(o)=1 and o[1][@name='@']]

I believe it should cover all the possible cases

[h1alexbel]

@maxonfjvipon How about these cases:

# No comments.
[] > test
  # No comments.
  [] > @
    if. > @
      a
      42
      88

I think, sparse-decoration should warn about test only here (@ should be good).

And this:

# No comments.
[] > test
  if. > @
    a
    42
    88

Here, no warnings should be issued. If this is correct, I propose the following XPath for detecting sparse decorations:

//o[(count(descendant::o[not(@base='Q.org.eolang.bytes')])=1 and o[@name='@'] and (not(@base) or @base!='^') and not(o[@base='∅'])) or count(o[@name='@' and o[@name='@']])>0]

This will handle cases above. WDYT?

[maxonfjvipon]

@h1alexbel check this, let's wait for the answer

[maxonfjvipon]

@h1alexbel here's more about sparse-decoration